A truck plowed through a Christmas market in Germany's capital on Monday evening, killing at least nine and injuring 50, a spokesman for the Berlin police said.

The incident happened at Breitscheidplatz, a public square in the center of Berlin. The driver's nationality wasn't known, but police said his truck appeared to have Polish license plates.

The driver attempted to flee but was apprehended by police, they added.

Berlin police later said on Twitter that a suspect was arrested in the vicinity of the public square, but whether that person was the driver of the truck remained under investigation.

A passenger in the truck was among those killed, police spokesman Thomas Neuendorf said on German TV. The passenger died at the scene, Berlin police said in a post on Twitter. It immediately wasn't clear how the passenger died, or the relationship to the driver.

It wasn't clear whether the truck veered into the holiday crowds on purpose or by accident. But local German media cited police who said initial indications pointed to an attack, not a traffic accident. NBC News could not immediately confirm those reports.

Berlin police said on Twitter that the motives of the attack were so far unclear and a criminal investigation team was onsite.

Witnesses said victims were crushed by the truck.

Last July, a truck driver killed 84 Bastille Day revelers in Nice, France, and injured more than 200, before he was shot dead by police. Officials said he had been planning the attack for months.

U.S. intelligence officials told NBC News this incident was somewhat consistent with the truck attack in Nice, but they are aware of no claims of credit and are not ready to call this a terrorist attack. They point out for context that the Germans have conducted a series of raids in recent weeks, rolling up ISIS operatives.

U.S. officials have long feared truck attacks on American soil. Permanent truck barriers were installed around government buildings nationwide after the 1995 truck bomb attack in Oklahoma City.

"While extremists have carried out attacks in Belgium, France, Germany, and Turkey in the past year, the Department remains concerned about the potential for attacks throughout Europe," the State Department said in a statement. "U.S. citizens should exercise vigilance when attending large holiday events, visiting tourist sites, using public transportation, and frequenting places of worship, restaurants, hotels, etc."

The Christmas market at Breitscheidplatz, close to the Kaiser-Wilhelm-Church, is just off the main shopping West Berlin district and is one of dozens Christmas markets in the city.

The Cedar Falls Tigers are headed back to the Girls State Basketball Tournament for the 4th consecutive year, following a 62-40 victory over Dubuque Hempstead Wednesday night in a Class 5A Regional Final in Cedar Falls. The Tigers opened the game on a 9-0 run and never looked back. Cynthia Wolf led Cedar Falls with 14, while Kamryn Finley added 11. The victory pushed the CF season record to 22-1, as the Tigers hope to get back to the 5A Championship game. West Des Moines Valley be...More >>

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